Such a hydraulic pump assembly can be used in a system including a wet disc coupling for distributing torque between front and rear axles of an all wheel drive vehicle (AWD) and/or between left and right wheels of a two or four wheel drive vehicle. This hydraulic pump assembly for actuating a wet disc coupling is shown and described in WO 2010/019094 and in a more developed form in WO 2011/043722. For a better understanding of the background of the invention, reference is made to these two publications, especially the latter.
A desirable property of an all wheel drive system and its actuator is high dynamics. Based on vehicle dynamical and traction optimizing desired values, it shall be possible to reach the desired torque as quickly as possible. The accuracy with which this is obtained shall also be as high as possible without creating superimposed disturbances, i.e. overtones of any kind to the fundamental signal.
A pressure regulator and thus torque regulator of the type shown in the above publications has basically a highly dynamic function. There is an inherent risk that it may react in a non-desirable way on process disturbances that are caused by for example external acceleration, vibrations, temperature changes, and rotation speed variations. As a result superimposed torque variations in a non-desired frequency range may occur.
It may thus be desirable to introduce control over the dynamics of the regulator in a defined frequency range in order not to be forced to make a balance between high dynamics and robustness against process disturbances.